Alkene metathesis (olefin metathesis) is a reaction between alkenes or olefinic groups, in which formally alkylidene groups are exchanged between the alkenes or olefinic groups. Examples of metathesis reactions include cross-metathesis, i.e. the reaction between two different olefins forming a new olefin or new olefins, the ring opening metathesis of a cyclic diene, which may also proceed under polymerization, the ring closing metathesis of a diene, the ethenolysis of an olefin having an internal olefinic double bond to form olefins having a terminal olefinic double bonds, and the formation of internal olefin(s) from terminal olefin(s) via homo-metathesis reactions.
US 2011/007742 generally discloses catalysts and processes for the Z-selective formation of internal olefin(s) from terminal olefin(s) via homo-metathesis reactions. The method includes reacting a first molecule having a terminal carbon-carbon double bond and a second, identical molecule via a homo-metathesis reaction to produce a product having an internal carbon-carbon double bond, wherein the internal carbon-carbon double bond of the product includes one carbon atom from the terminal double bond of the first molecule and one carbon atom from the terminal double bond of the second carbon atom, and wherein at least 60% of the internal double bonds of the product are formed as the Z-isomer.
Further compounds based on molybdenum and tungsten and useful as catalysts in metathesis reaction are disclosed in U.S. Pat. No. 6,121,473, US 2008/0119678 and US 2011/0015430. Such catalysts usually are applied or have to be applied in a metathesis reaction in a relatively high molar amount with respect to the molar amount of olefin or olefins in order to achieve a sufficient degree of conversion of the olefin(s) used as starting material. A molar ratio up to 1:500 with respect to the applied olefin(s) (molar ratio catalyst to olefin(s)) may be necessary to achieve a conversion of 30% or more. And because these catalysts may be relatively expensive to make, such low-conversion reactions may not be cost-effective at an industrial scale, and thus may lack industrial applicability. Further, such compounds may be more susceptible to degradation in the presence of certain atmospheric gases. Therefore, they may be difficult to use at a larger scale in an industrial process, where larger quantities may be needed.
Therefore, there is a continuing need to develop organometallic compounds that are stable and that provide relatively high conversion at low catalyst concentrations.